This invention relates generally to improvements in fuel systems and related controllers for use in gas turbine engines. More particularly, this invention relates to a fuel control system and method for scheduling fuel supply to a turbine engine during a deceleration condition to permit maximum rate deceleration without risk of combustor blowout.
Gas turbine engines are well known in the art and generally comprise a turbocompressor rotating group in association with a combustor. A compressor stage at one end of the turbocompressor rotating group draws in and compresses air for supply to the combustor for appropriate combustion with fuel. The resultant hot and high energy gases of combustion are directed in driving association with a compressor stage at the opposite end of the turbocompressor rotating group. Engine work output is obtained by mechanical drive means coupled to the rotating shaft of the turbocompressor rotating group, and/or by passing the combustion gases from the turbine stage through an appropriate thrust nozzle.
In some operating environments, the gas turbine engine is subjected to relatively rapid transient speed conditions, wherein combustor blowout or flameout can occur. In particular, during a rapid engine deceleration phase, the fuel supply to the combustor is rapidly curtailed. If the fuel supply to the combustor, in relation to the corresponding air flow provided by the compressor stage, falls below a minimum level for even a brief interval, there is a substantial risk that the combustor flame will be extinguished. This prospect of combustor blowout is, of course, extremely undesirable especially in gas turbine engines used to power aircraft.
In the past, substantial design effort has focused upon improvements in fuel controls for regulating the supply of fuel to the combustor of a gas turbine engine. Such fuel controls have been adapted for response to numerous engine operating parameters in an attempt to optimize combustor fuel flow throughout a range of engine operating conditions. For example, prior fuel controls have responded to parameters such as aircraft altitude, ram air effects, air temperature, etc. However, other variables such as part-to-part variations in combustor performance and stability and other mechanical engine influences have complicated the design of fuel controls, especially in response to a rapid deceleration condition. To prevent fuel control overshoot and resultant risk of combustor blowout during deceleration, prior fuel controls have generally functioned by attempting to limit the rate at which engine deceleration can occur.
The present invention provides a significant improvement upon fuel control systems and related methods for scheduling fuel supply to a gas turbine engine during a deceleration condition, wherein the fuel control system is responsive to a small number of parameters to accommodate deceleration at a substantially maximum rate but without risk of combustor blowout.